In recent times there have been a rapidly increasing number of sustainable buildings entering the real estate market. Many of these buildings differ considerably with respect to their sustainable features, either from a design and/or performance basis, although a wide range of sustainable building assessment tools are now promoted and readily available throughout the world. Unfortunately many of these tools differ considerably with regards to what they actually assess, how they operate and whether they can be compared directly with assessment tools from other countries. This paper undertakes a unique international assessment of global sustainability tools and critiques their individual strengths and weaknesses. Most importantly the focus is placed on which tools from different countries can be directly compared with each other i.e. is a five star building with one rating system directly comparable with another rating system. The results of this paper will lessen much of the confusion and uncertainty that accompanies assessment tools for sustainable buildings, which in turn will assist investors, developers, tenants and government bodies to make informed decisions about green buildings. In addition it is envisaged that removing some of the uncertainty associated with sustainable buildings will increase the transparency for stakeholders and assist them to embrace sustainable buildings with more confidence.